Electronic devices, such as organic thin-film transistors (OTFTs) and other organic semiconductors (OSCs) have attracted a great deal of attention because of their potential applications in low-cost, large-area and flexible electronics. Organic semiconductors are commonly referred to as either p-channel (hole-transporting) or n-channel (electron-transporting) depending on which type of charge carrier is dominant for the charge transport.
While organic semiconductors have been readily implemented for a variety of applications, both p-channel and n-channel organic semiconductors have been challenging to manufacture and implement in the context of various applications. For instance, the energetically high-lying lowest unoccupied molecular orbital (LUMO) levels in most organic semiconductors hinder the efficient injection of electrons. n-Type doping can be applied to increase the electron density and improve the electron injection in semiconductor devices. In n-channel OTFTs with efficient doping, electrons can be transferred from the high-lying highest occupied molecular orbitals (HOMOs) of dopants to the LUMOs of organic semiconductors by n-type doping. However, such dopants are susceptible to oxidation in air.
While various n-type dopants have been used with organic semiconductors, many have been challenging to implement. For example, alkali metals are prone to diffuse through organic layers due to their relatively small atomic radii, leading to device instability. In addition, alkali metals are difficult to process. Other dopants having both extremely high-lying HOMO levels and exhibiting air stability do not provide donors that are strong enough to obtain sufficient conductivity. In addition, the accessibility and implementation of dopants exhibiting low-lying LUMO energy levels has also been limited, and in particular for organic applications.
These and other issues remain as a challenge to a variety of methods, devices and systems that use or benefit from semiconductors.